The proliferation of mobile devices incorporating displays, such as mobile phones, continues as the feature sets associated with these devices expand and improve. In the past, the display portion of the mobile device was mainly focused on allowing a user to select certain features of the mobile device. However, current growth in display and related technologies are moving the role of the display to become much more of a central feature of the mobile device.
The majority of mobile devices use a liquid crystal display (LCD). A popular form of LCD is a flat display, which typically consists of an array of red, green and blue color pixels that are arranged in front of a light source called a backlight. Each pixel contains a series of liquid crystal molecules arranged between two transparent electrodes and two polarizing filters having orthogonal polarizing directions. With no electric charge applied between the two electrodes, the liquid crystal molecules are oriented to prohibit the transmission of backlight.
Applying a charge, however, provides a reorientation of the liquid crystals that is proportional to the applied charge. This allows a proportional amount of backlighting to be transmitted through the pixel area. The amount of backlighting transmitted by a pixel determines a brightness of the image in that pixel area, as seen by an observer. The contrast associated with the image on the display corresponds to the range of actual backlighting transmitted by all pixels that compose the image. This range is typically a portion of the full range that is possible between zero and full reorientation of the liquid crystals. Therefore, an image rendered by the LCD is a function of the brightness, contrast and backlight intensity associated with the image.
An image histogram is a plot of the number of pixels associated with each brightness value actually occurring in the image. These brightness values typically range from zero to 255 along a brightness scale corresponding to eight bits of resolution. A brightness value of zero corresponds to the blackest black and a brightness value of 255 corresponds to the whitest white that are possible on a particular LCD. This histogram provides a luminance “finger print” for its corresponding image.
The demand for higher quality images is increasing. The quality of an image provided by an LCD is directly proportional to the number of pixels employed in the display. Additionally, the intensity of the backlight is often set as high as possible to make the display visible in high ambient light conditions, such as bright sunlight.
The amount of power used by the mobile device is a critical factor associated with most mobile devices, since size and weight constraints typically place severe restrictions on battery sizes. Currently, backlight power requirements for the LCD consume approximately 30 percent of the available battery power in a mobile phone. As mobile displays employ a more central role in more mobile devices, backlight power will become an even more critical issue.
Accordingly, what is needed in the art is a more power-efficient way of rendering images on a mobile LCD.